Objective: To investigate the relationship between the changes of serotonin metabolism and the hot flushes in climacteric women.Methods.Ninety eight climacteric women, aged 40-60, were enrolled and divided into 4 groups: Group A: 20 cases of early menopausal transition.Group B: 26 cases of late menopausal transition, with skip of periods 3-12 months.Group C: 28 cases of early postmenopause (1-3 yrs).Group D: 24 cases of late postmenopause(＞3-6 yrs).Twelve normal women of reproductive age (24±3yrs) were served as young controls.Fifty two postmenopausal women were subdivided into 3 groups according to the presence or the absence of hot flushes: (1) postmenopausal controls without hot flushz 17 cases, (2) mild hot flushes group: 20 eases,fewer≤5 times/d, (3) severe hot flushes group: 15 cases, more than 5 times/d.Plasma concentrations of tryptophan (TP), 5-hydroxytryptophane (5-HTP), 5-hydroxytryptamine (5-HT or serotonin), 5-hydroxyindoleacetic acid (5-HIAA) and luteinizing hormone (LH) were measured in all participants by high pressure liquid chromatography-fluorescence spectrophotometer (HPLC-FS).The relationship between serotonin metabolic parameters and menopause, hot flushes were analysed.Results: (1) Mean 5-HT and 5-HIAA concentrations in plasma were significantly higher in climacteric women than those in young controls, especially in Group B.Mean 5-HTP and 5-HT levels were higher and 5-HIAA lower in Group D as compared with those of young controls.(2) Plasma 5-HT levels was positively correlated to luteinizing hormone concentration in postmenopansal women (P＜0.01).(3) In the mild hot flushes group, only plasma 5-HTP levels were significantly higher than that in the non-hot flushes group.In severe hot flushes group,plasma 5-HT and 5-HTP contents were significantly higher and 5-HIAA/5-HT ratio lower than those in the non-hotflushes groups.Conclusion: The results suggest that the catabolic disorder of serotonin maybe involve in the underling mechanism of hot flushes in postmenopausal women.